The illumination system is a very important part of a microscope. In fact, the full potential of any optical microscope can only be achieved if the microscope is equipped with the proper kind of illumination system. Specimen illumination also affects operator comfort and efficiency.
It is difficult to determine the best illumination system to achieve optimum illumination, since this depends both on the nature of the specimen to be examined and the type, structure and design of the microscope. For example, the illumination problem is compounded in the case of a stereo microscope, which embodies two separate and complete microscopes. No single illumination system is suitable for examining all types of specimens. Often, different illumination systems are used with the same microscope for different types of specimens. Almost always, there is an optimum illumination system for a particular system.
Various types of illumination systems are known, including, but not limited to the following: Nicholas illuminator, general purpose illuminator, fluorescent illuminator, reflector illuminator, ring illuminator, spot illuminator, coaxial illuminator, eyepiece illuminator, fiber optic annular illuminator, fiber optic bifurcated illuminator, fiber optic four-point illuminator, critical illuminator, and Koehler illuminator. Regardless of the type of illuminator, they all have one thing in common - an illumination element. Some use incandescent lamps, others fluorescent lamps, and some use fiber optics. It is often necessary and/or preferable to vary the intensity of the illumination provided by the light source. Often, this is accomplished by varying the voltage applied to the illumination element by way of an electrical rheostat. Unfortunately, rheostats are relatively expensive and can be bulky.
There is a need, then, for a device for controlling illumination in microscopes and in other devices which does not require an expensive, bulky electrical rheostat.